The present invention relates to implantable, expandable, multicontact electrodes. In a preferred embodiment, such electrodes comprise deployable, paddle-type, multicontact electrodes useful for spinal stimulation.
There are two major types of electrodes used for spinal stimulation: (1) percutaneously implanted in-line electrodes/leads requiring local anesthesia for implant, and (2) paddle-shaped electrodes requiring major surgery for implantation.
The first type of electrodes, i.e., the in-line electrodes, comprise thin, rod-type electrodes. Such in-line or rod-type electrodes are easy and less invasive to implant, typically requiring only local anesthesia and the use of a large gauge needle. Disadvantageously, such in-line electrodes are not as stable as paddle leads, and are prone to migration.
The second type of electrodes, i.e., the paddle-shaped electrodes, provide a large-area electrode surface to contact the body tissue, much like a miniature ping-pong paddle. Advantageously, such paddle-type electrodes are more effective and stable than in-line electrodes. Moreover, such paddle-type electrodes provide a platform for multiple electrodes in many possible configurations to thereby optimize electrode programming and clinical results. In contrast, the percutaneous in-line electrodes can only combine electrodes in a vertical row. Disadvantageously, however, the paddle-type electrodes require complex major surgery for implantation, along with all the attendant risks associated with major complex surgery.
It is thus evident, that there is a need in the art for an electrode which can deliver the maximum advantages of the paddle-type electrodes, but without requiring extensive surgery for implantation.
The present invention addresses the above and other needs by combining the advantages of both the paddle-type electrode and the in-line (rod-type) electrode. That is, the present invention provides an implantable electrode or electrode array that may be implanted like a percutaneously inserted lead, i.e., without requiring major surgery, but once inserted, expands to provide a platform for many electrode configurations.
In accordance with one important aspect of the invention, an electrode array is provided on a flexible, foldable, subcarrier or substrate. Such subcarrier or substrate is folded, or compressed, during implantation, thereby facilitating its insertion using percutaneous implantation techniques. Once implanted, such subcarrier or substrate expands, thereby placing the electrodes in a desired spaced-apart positional relationship, and thus achieving a desired electrode array configuration.
In accordance with another aspect of the invention, the substrate or subcarrier of the electrode array includes a memory element which causes the electrode array to expand or unfold to a desired configuration after the electrode array has been implanted while in a folded up or compressed state.
In accordance with yet another aspect of the invention, the electrode array includes a membrane as an integral part thereof that prevents ingrowth of tissue inside the electrode array, thereby facilitating repositioning, removal, and/or reinsertion of the electrode array, as required.
In one embodiment, the invention may be characterized as a system for implanting an expandable electrode array. Such system includes an electrode array and an insertion tool. The electrode array comprises (a) a flexible substrate, (b) a plurality of parallel columns of spaced-apart electrodes integrally formed on a surface of the flexible substrate, and (c) means for making electrical contact with each electrode in each of the plurality of parallel columns of electrodes. The flexible substrate normally assumes a planar flat shape, but is configured so that it may be collapsed or folded so as to assume a folded or compressed state. The insertion tool comprises a hollow tube or hollow needle wherein the electrode array may be placed while in its folded or compressed state.
In order to implant the electrode array, the hollow tube or needle (with the folded or compressed electrode array therein) is injected into the living tissue of the desired implant site. The folded electrode array is then expelled from the hollow tube and allowed to assume its expanded or unfolded state within the tissue.
It is thus a feature of the present invention to provide a foldable, paddle-type electrode which can be implanted using a simple, needle-type tool without major surgical intervention.
It is a further feature of the invention to provide a loading tool that assists with the folding and inserting of the paddle-type electrode into an insertion tool.
It is yet another feature of the invention to provide a simple method of implanting a foldable, paddle-type electrode that does not require major surgical intervention.